1. Field of the Invention
The present invention generally relates to a plastics granulating method, and particularly relates to a novel improvement of the plastics granulating method in which a pressure medium is supplied to move the cutter drive shaft forward/backward so that knives or the like can be automatically and easily controlled to adjust the contacting state between the knives and the die surface.
2. Description of the Related Art
Conventionally, various plastics granulating apparatus have been used. A typical device is disclosed in Japanese Patent Unexamined Publication No. Hei-1-22551, as shown in FIGS. 2 and 3.
In the drawings, reference numeral 1 designates a granulating machine. The granulating machine 1 is constituted by a manifold 2 for circumferentially distributing melted resin extruded from an extruding machine (not shown), a die 3 attached on the manifold 2 to be in close contact therewith, a cutter casing 4 attached on the die 3, and a cutter 5 provided in the cutter casing 4.
The die 3 is disc-shaped, and a large number of nozzles 6 are formed axially through a ring-like region of the die 3 surrounding the center of the same. Both ends of each nozzle 6 are opened into a ring-like resin path 2a of the manifold 2 and into the cutter casing 4, respectively.
The cutter casing 4 is removably fixed on the manifold 2 through bolts 7 to be in close contact with the surface of the die 3. The cutter casing 4 has a hot-water inlet 8 and a hot-water outlet 9 to allow hot water to be introduced therein.
The cutter 5 has a configuration so that a plurality of cutter knives 11 are radially fixedly supported on the outer circumference of an end surface of a cutter holder 10 facing the die 3. The cutter knives 11 are provided in opposition to a die surface 3a of the die 3, that is, in opposition to the surface of the ring-like region through which the nozzles 6 are formed. A rotary force is transmitted to the cutter holder 10 through a cutter drive shaft 12 disposed on the central axial line of the cutter holder 10.
The cutter drive shaft 12 is rotatably supported in a cylindrical casing 13 through bearings 14 and is fixed axially with respect to the casing 13. The casing 13 is axially slidably supported by a housing 15 fixed on the back surface of the cutter casing 4. Therefore, the cutter drive shaft 12 is axially movable together with the casing 13. A fine adjustment mechanism 19 constituted by a worm 16, a worm wheel 17, and adjustment screws 18 is provided between the housing 15 and the casing 13 so that the casing 13 can be axially moved by the rotation of the worm 16. A compression spring 20 is provided between a rear end portion (a right end portion in FIG. 2) of the casing 13 and the housing 15 to urge the casing 13 and the cutter drive shaft 12 against the die 3 to minimize axial play of the cutter driving shaft 12 due to gaps of the bearings 14, play of the screws of the fine adjustment mechanism 19, or the like.
The base end of the cutter drive shaft 12 is coupled with an output shaft 22 of a rotary machine (not shown), such as an electric motor or the like, through a coupling 21 which allows rotary movement of the cutter drive shaft 12.
A gap portion between the base end portion of the cutter drive shaft 12 and a housing portion 15a surrounding the base end portion is sealed by a pair of front and rear sealing members 23 and an oil reservoir 24 is formed in the gap portion. The oil reservoir 24 is communicated with an oil chamber 27 on the small-diameter piston 26 side of a booster 25 provided outside the housing 15. High pressure air is fed from a pressure air source (not shown) into a pressure chamber 29 on the large-diameter piston 28 side of the booster 25 through a change-over valve 30, a reducing valve 31, and an air valve 32. The change-over valve 30 is configured so that the pressure chamber 29 of the booster 25 is opened into the atmosphere when the change-over valve 30 is switched to the illustrated position and the pressure chamber 29 and the reducing valve 31 are communicated with each other when the change-over valve 30 is switched to the right position.
An oil hole 33 is formed in the base end portion of the cutter drive shaft 12 to be opened into the oil reservoir 24 provided in the surrounding of the base end portion. An oil path 34 is formed through the central portion of the cutter drive shaft 12 from the front end surface thereof, that is, the end surface at the die 3 side, to the oil hole 33 of the base end portion.
Next, as shown in FIG. 3, the cutter holder 10 has portions which are substantially conical and cylindrical in shape respectively, and is configured so that a front end portion of the cutter drive shaft 12 is slidably fitted into the cutter holder 10 and an O ring 35 is provided between the inner circumferential surface of the cutter holder 10 and the outer circumferential surface of the cutter drive shaft 12. Further, a blanking cover 37 is attached on the end surface of the conical portion of the cutter holder 10 at the side of the die 3 through a gasket 36, and an oil-tight closed chamber 38 is formed between the cutter holder 10 and the front end surface of the cutter drive shaft 12. Pressurized oil is fed into the closed chamber 38 through the oil path 34 formed in the cutter drive shaft 12.
A torque transmission disc plate 40 having an involute spline 39 formed in its outer circumferential surface is fixed on the front end surface of the cutter drive shaft 12. A torque transmission ring 42 having an involute spline 41 formed in its inner circumferential surface, on the other hand, is fixed on in the cutter holder 10. Consequently, by making the splines 39 and 41 engage with each other, the rotary force from the cutter drive shaft 12 is transmitted to the cutter holder 10 and the cutter holder 10 is supported so as to be slidable relative to the cutter drive shaft 12.
Compression springs 43 are provided between the torque transmission disc plate 40 fixed on the front end surface of the cutter drive shaft 12 and the cutter holder 10 so that the cutter holder 10 is always urged downward by the springs 43, that is, in the direction tending to separate the cutter holder 10 from the die 3.
Next, the operation of the cutter position adjustment device in the conventional granulating apparatus will be described.
First, when the die 3 is cleaned, the cutter knives 11 replaced, or the like, the housing 15 is mounted on a truck 44 as shown by a phantom line in FIG. 2, and the bolts 7 coupling the cutter casing 4 and the die 3 with each other are removed. Then, the truck 44 is made to move so that the whole cutter device constituted by the cutter casing 4 and the housing 15 can be separated from the die 3. As a result, since a sufficient working space can be secured between the die 3 and the cutter 5, the cleaning, replacement, or other operations can be performed.
After completion of the work, the cutter casing 4 is placed in contact with the die 3 and fixed thereon through a procedure reverse to the foregoing, and adjustment of the cutter position can be performed while the extruding machine is in the stopped state.
To perform the positional adjustment, first, the fine adjustment mechanism 19 is operated to thereby retreat, to the maximum extent, the cutter drive shaft 12 together with the casing 13. Next, the air valve 32 is opened and the change-over valve 30 is switched to the right position, so that air having pressure adjusted by the reducing valve 31 is led into the pressurized chamber 29 of the booster 25, and pressured working oil is sent from the oil chamber 27 of the booster 25 into the oil reservoir 24 in the surrounding of the base end portion of the cutter drive shaft 12. Then, the high-pressure working oil flows into the closed chamber 38 provided on the front end side of the cutter drive shaft 12 through the oil hole 33 and oil path 34 formed in the cutter drive shaft 12. As a result, the cutter holder 10 advances toward the die 3, and the cutter knives 11 come close to the die surface 3a.
When the cutter holder 10 advances to the cutter drive shaft 12 through a full stroke, the cutter holder 10 abuts on the torque transmission disc plate 40 fixed on the front end surface of the cutter drive shaft 12 as shown in FIG. 3 so that the cutter holder 10 is prevented from further advancement. Then, the fine adjustment mechanism 19 is operated in this state to thereby make the cutter 5 slightly advance together with the cutter drive shaft 12 and the casing 13 to adjust a gap between the cutter knives 11 and the die surface 3a. When the cutter knives 11 are urged against the die surface 3a, the cutter knives 11 are made to closely contact with the die surface 3a, and the pressure in the closed chamber 38 is adjusted by the reducing valve 31.
After completion of the positional adjustment of the cutter 5, the change-over valve 30 is switched to the illustrated position so that the pressure chamber 29 of the booster 25 is opened to the atmosphere. As a result, the pistons 26 and 28 in the booster 25 are movable to thereby reduce the pressure in the closed chamber 38. Then, the cutter holder 10 is retreated by the urging force of the compression springs 43 until the blanking cover 37 abuts on the torque transmission disc plate 40 provided on the front end surface of the cutter drive shaft 12. As a result, the cutter knives 11 are sufficiently separated from the die surface 3a as shown in FIG. 2.
Next, when granulation is to be performed, the change-over valve 30 is switched to the right position to thereby supply high-pressure air into the pressure chamber 29 of the booster 25. As a result, the cutter knives 11 advance to the first set position. Next, the extruding machine is operated, and the cutter drive shaft 12 is driven to rotate by a rotary driving device such an electric motor or the like through the coupling 21. Then, the rotary force is transmitted to the cutter holder 10 through the splines 39 and 41, so that the cutter knives 11 rotate along the die surface 3a. Therefore, melted resin continuously extruded from the extruding machine through the resin path 2a and the nozzles 6, 6, . . . of the die 3 is finely cut by the cutter knives 11, and processed so as to be granulated. The thus processed resin pellets are solidified in hot water in the cutter casing 4, and discharged from the hot water outlet 9 together with hot water.
Having such a configuration as described above, the conventional plastics granulating apparatus has the following disadvantages.
(1) It is generally necessary to exchange the cutter knives every 1-3 months. The configuration has been made such that the oil path 34 is formed in the cutter drive shaft 12 and the contact state between the cutter knives 11 and the die surface 3a is changed by changing the pressure in the closed chamber 38 formed in the cutter holder 10. It is necessary to assemble the cutter knives 11 in a precise manner. Therefore, under the condition that the cutter holder 10 is mounted to the cutter drive shaft 12, it is difficult to assemble the cutter knives 11. In general, when the cutter knives 11 are assembled, the cutter holder 10 is dismounted from the cutter drive shaft 12. It has been therefore necessary to remove the blanking cover 37 of the cutter holder 10 at the time of exchange of the cutter knives 11, and the removal of the blanking cover 37 allows oil in the oil path 34 to leak outside to thereby make the exchanging work very difficult. PA1 (2) The limit of the life of the cutter knives 11 is about 2 mm in term of the abrasion thereof. If the abrasion exceeds the limit, the contact width of the edge surface increases to thereby result in defective cutting of the extruded melted resin. The abrasion state of the cutter knives 11 is therefore related to the quality of the pellets produced. In the conventional configuration, however, the abrasion state of the cutter knives 11 cannot be observed from the outside during continuous operation thereof. Accordingly, the machine must be stopped, the bolts 7, coupling the cutter casing 4 and the die 3 with each other, removed to separate the whole cutter device from the die 3, and the truck 44 retreated to separate the die 3 and the housing 15 from each other, to visually inspect the abrasion state of the cutter knives 11. PA1 (3) Further, in use, the high-pressure of air adjusted to have a predetermined pressure by the reducing valve 31 in advance is converted into oil pressure in the booster 25 prior to the start of rotation of the cutter knives 11, and then the pressurized oil is fed into the closed chamber 38 through the oil reservoir 24 and the oil path 34 to thereby urge the cutter holder 10 toward the die 3 so that the cutter knives 11 are urged against the die surface 3a by the predetermined pressure and are then subsequently rotated.
Further, since it is necessary to prevent air from entering the oil path 34 when the cutter holder 10 is mounted, maintenance is expensive and time consuming.
If the cutter knives 11 are made to start rotation to thereby cut melted resin continuously extruded from the nozzles 6 in hot water led into the cutter casing 4, the cutting angle of the cutter knives 11 generates a thrust force in the cutter knives 11 tending to urge the cutter knives 11 toward the die surface 3a due to the rotation of the cutter knives 11. The thrust force changes in proportion to the rotational speed. That is, the thrust force becomes large as the rotational speed becomes high.
The contact pressure between the cutter knives 11 and the die surface 3a is increased by the thrust force, and if the contact pressure exceeds a predetermined value, the cutter knives 11 are rapidly worn to thereby shorten the life thereof.
The compression springs 43 are therefore interposed between the torque transmission disc plate 40 fixed on the front end surface of the cutter drive shaft 12 and the cutter holder 10 so that the urging force of the compression springs 43 acts against the thrust force to thereby prevent the contact pressure between the cutter knives 11 and the die surface 3a from exceeding an abrasion limit value in use as described above.
With the conventional configuration, however, it has become impossible to cope with a recent tendency to increase the size of the extruding machine and increase in the rate of pellets produced. That is, the thrust force to be generated in the cutter knives 11 becomes larger and larger because of the increase in size of the cutter holder 10, the increase in number of the cutter knives 11, and the increase in rotational speed of the cutter knives 11 has rendered it impossible to provide a spring having a sufficient force against the increased thrust force, in the cutter holder 10, because of the limitation in the mounting space. As a result, the thrust force due to the rotation exceeds the allowable capability of the compression springs 43 so that the cutter knives 11 are urged against the die surface 3a by abnormal pressure to thereby promote the abrasion of the cutter knives 11 and to shorten the life thereof.
Also, since fluid pressure is applied to the rotating cutter holder 10 through the oil path 34 formed in the rotary cutter drive shaft 12, the device is exceedingly complicated so that problems such as oil leakage or the like often develop and maintenance is expensive and time consuming.